1. Field of the Invention
The present invention relates to the plunger of a fuel injection pump of a diesel engine, and more particularly to a fuel injection pump plunger which enables the timing of the fuel injection to be controlled and facilitates engine performance recovery when the engine is running under full load.
2. Description of the Prior Art
In a conventional fuel injection pump of a diesel engine, fuel is sucked in and expelled under pressure by the reciprocating action of a plunger in a fuel chamber formed in the plunger barrel.
Adjustment and control of the timing at which the injection of the fuel is started and stopped are done by providing upper and lower leads in the head of the plunger and adjusting the relative positional relationship between these leads and the fuel intake and exhaust port formed in the barrel.
More specifically, the head of the plunger is provided with a sloping lower lead and a longitudinal groove which connects the lower lead to the plunger chamber. When the accelerator is pressed, the timing of the end of the fuel injection operation is controlled by rotating the plunger by an amount corresponding to the depression of the accelerator, changing the relative positional relationship between the lower lead and the fuel port. As such, this can be used to control the fuel injection amount.
An upper lead is formed sloping down from the upper face of the plunger facing the plunger chamber at a position of vertical opposition to the lower lead. When the accelerator is pressed, the timing of the start of the fuel injection operation is controlled by rotating the plunger by an amount corresponding to the depression of the accelerator, changing the relative positional relationship between the upper lead and the fuel port. As such, this can be used to control the fuel injection timing.
In addition, engine noise can be reduced by adjusting the upper lead to retard the timing of the fuel injection by an amount corresponding to the engine load. In rapid idling regions (meaning regions in which exceeding the rated engine speed causes the governor mechanism to reduce the fuel injection amount), however, this gives rise to a smokey exhaust caused by fuel which has not undergone complete combustion being emitted through the still-open exhaust port.
JP-B-55-28863 is an example of a disclosure of a fuel injection pump arrangement which uses this type of upper lead arrangement to control the timing of the fuel injection, reduce engine noise and prevent the emission of exhaust smoke. However, another problem that arises when an upper lead arrangement is the sole means used to reduce noise and prevent a smokey exhaust is that under full-load conditions it increases the time it takes a diesel engine to come back up to speed. That is, although under full-load conditions it is preferable to produce a rapid recovery in the engine speed by increasing the fuel injection rate and advancing the timing of the fuel injection, with the above upper lead arrangement the fuel injection timing remains retarded even under full-load conditions, so the engine therefore takes longer to regain its speed.
An object of the present invention is therefore to provide a fuel injection pump plunger which enables the timing of the fuel injection to be controlled in accordance with the engine load and without using a conventional timer arrangement based on a lead provided in the plunger head. The fuel injection pump plunger according to the present invention prevents the production of exhaust smoke at high idling speeds, provides quieter engine operation under partial loads and during full-load operation enables the engine to regain speed more rapidly.
The above object is attained with a fuel injection pump plunger according to the present invention which moves reciprocally within the plunger chamber to suck in fuel through a fuel port in the barrel and expel the fuel from a fuel outlet, comprising forming in the head of the plunger a sloping lower lead, a longitudinal groove which connects the lower lead to the plunger chamber, and an upper lead formed sloping down from the upper face of the plunger facing the plunger chamber at a position of vertical opposition to the lower lead, and an orifice portion in the form of a flat or the like which extends parallel with the axis of the plunger and connects the end of the upper lead to the plunger chamber and enables the injection timing to be advanced.
In the fuel injection pump plunger thus configured, the upper and lower leads are used to effect a fuel injection timing (starting and stopping) control which corresponds with the engine load, and, if required, can be used to reduce engine noise and prevent the production of exhaust smoke.
Moreover, the orifice constituted by a flat or the like provided at the end of the upper lead makes it possible to suppress retardation of the fuel injection timing when the engine is running under a full-load condition.
Thus, in contrast to an arrangement in which only an upper lead is provided and there is no orifice portion so the timing of the closing of the fuel port (the start of the fuel injection) is therefore determined solely by the position of the upper face of the plunger, giving rise to large variations in the effective fuel delivery stroke, the provision of the orifice portion after the end of the upper lead in accordance with the present invention makes it possible to suppress extreme changes in the effective stroke, and as a result it is possible to suppress degradation of engine recovery when the engine is running under full-load conditions. In addition, adjusting the plunger prestroke is facilitated by enabling the orifice portion to be used for the adjustment.
Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and following detailed description of the invention.